London, Oct 11 A Boeing chief has suggested that the company’s mysterious unmanned space-plane, called X-37B, developed for the US Air Force, could be scaled up and modified to carry astronauts.

The company’s X-37B project chief Art Grantz revealed that at least two more versions of the 9-metre long space-plane are under investigation – one of which involves adding a crew to a much-enlarged version of the space drone, New Scientist reported.

If built, the new version would give the US back its ability to shuttle people to the International Space Station."

The X-20 Dyna-Soar ("Dynamic Soarer") was a United States Air Force (USAF) program to develop a spaceplane that could be used for a variety of military missions, including reconnaissance, bombing, space rescue, satellite maintenance, and sabotage of enemy satellites. The program ran from 24 October 1957 to 10 December 1963, cost US$660 million ($4.73 billion today[1]), and was cancelled just after spacecraft construction had begun.